1. Field of the Invention
This invention relates to a process for developing a silver halide photographic emulsion and, more particularly, to a process for developing a silver halide emulsion capable of forming a latent image in the inner portions of silver halide grains, to thereby directly form positive images.
2. Description of the Prior Art
Several photographic processes for directly obtaining positive (reversal) images through one development after imagewise exposure have been known. One of them is a process using a silver halide emulsion capable of forming latent images in the inner portions of the silver halide grains. According to this process, such a silver halide photographic emulsion (herein referred to as an internal latent image-forming silver halide emulsion) is imagewise exposed and subjected to uniform exposure or to the action of a nucleating agent such as hydrazine to form development nuclei on the grain surface, and then processed with a surface developer to obtain positive (reversal) images. This process is called an internal image-reversal process, the principles of which are described in, for example, The Theory of Photographic Process, 4th Ed., compiled by T. H. James (1977), p. 187.
The nucleating agent (or fogging agent) used for the internal image-reversal process is incorporated in a developer or a light-sensitive material, in particular, in a silver halide emulsion layer. As the nucleating agent, there are hydrazines such as described in East German Pat. No. 5,024, U.S. Pat. Nos. 2,563,785, 2,588,982, 2,604,440, 3,227,552, 4,030,925, 4,080,207, and Research Disclosure, 15164, pp. 76-77 (structural formulae I and II), hetero ring quaternary ammonium compounds such as described in U.S. Pat. Nos. 3,615,615, 3,718,470, 3,719,494, 3,734,738, 3,330,655, and 4,094,683. However, conventional nucleating agents have one or more defects especially when they are incorporated in a silver halide emulsion layer. They may not provide good photographic properties (in particular, a high Dmax/Dmin ratio), they may reduce the storage stability of the silver halide emulsion, negative images are liable to form particularly in high exposure portions, gases are generated upon photograhic processing which results in deterioration of image uniformity, the compounds lose their activity under some conditions due to their instability, they are liable to react with other emulsion additives and lose their activity, stain is formed in highlight exposure portions, a long induction period is required upon development or a sufficient developing rate is not attained, and synthesis of the compounds in the pure form is difficult.